A router system with a centralized switch fabric at its core requires that the entire switch be configured in an internally consistent way. A fabric is a collection of devices which cooperatively provide a general routing capability. In order to scale to a large router with several hundred ports, it is necessary to have a router switch fabric with uniform scaling properties. One example of a fabric with these properties is a centralized crossbar. Electrical crossbars typically have scalability limitations, limiting the size to tens of ports at a maximum. Previous IP routers have been unable to take advantage of optical switch technology due to their size and reconfiguration speed limitations. In order to utilize an optical switch for the fabric of an IP router, the fabric must be able to change configurations quickly enough to efficiently route the shortest IP packet, within on order of tens of nanoseconds. Present optical switch technology requires milliseconds for reconfiguration. Additionally, present optical switch technology is severely limited to just a small number of ports, such that an optical switch is unable to scale to large numbers of inputs and outputs.
In order to scale to larger systems, prior routers have resorted to distributed switching fabrics. These fabrics typically have multiple arbitration points to traverse the fabric, resulting in increased fabric latency and congestion hot spots within the fabric. Multiple packet forwarding modules are distributed around such a system in remote racks. The packet forwarding modules are responsible for organizing data packets from the input ports to be passed through the switch fabric.
In a future large router system, the number of input and output ports can reach several hundred. Packet forwarding modules are remotely distributed over a wide area. Complex switching is required, with long latency or delay times in passing information through the router system accurately with a high throughput. In such an environment, an arbitration system is needed to handle high data throughput and provide a consistently high connection rate of data with the switch fabric.